The radio frequency (RF) field that is intended to be sensed by an RF coil in a magnetic resonance imaging (MRI) system is of near nature i.e. the distance between the RF transmitter and the RF receiver is less than the wavelength of the signal that is to be sensed. The MRI system comprises an opening referred to herein as bore that receives the object that is to be imaged. Further, the MRI system comprises an RF shield around the bore, which influences the resonant frequency of the RF coil depending on the diameter of the bore and the distance of the RF coil from the center of the bore. For example, an RF coil tuned for a certain resonant frequency in a bore having a diameter of 60 cm exhibits a different resonant frequency in a bore having a diameter of 70 cm due to variation in the distance between the RF coil and the RF shield.
The RF coil comprises an inductive element and a capacitive element. The value of the inductive element is fixed and therefore in order to achieve tunability, the capacitive elements in the RF coil comprise combinations of fixed and mechanically variable capacitors.
Conventionally, the RF coils are tuned in an iterative manner, initially without load, then with load, and then in an RF shield simulator, by manually adjusting one or more tuning knobs of the variable capacitor.
Further, testing of an RF coil involves measuring return loss i.e, logarithmic equivalent of reflection coefficient of the RF coil and transmit signal decoupling between the RF transmitter and the RF receiver. This is a repetitive and time-consuming process, which is performed manually.
Hence there exists a need for a system and method for performing testing and tuning of the RF coils used in the MRI system, which is automatic, efficient and reliable.